Yes, they were actually discovered experimentally before neutrinos were.

>They are distinguished from neutrinos by their helicity (direction >of spin relative to their direction of motion). When a neutron decays, >for example, it yields a proton, an electron, and an antineutrino. >However, it seems to me that if neutrinos have rest mass, this >distinction must in principle lapse, since you can then choose a >frame of reference in which the helicity is reversed.